Messaging systems typically allocate message mailboxes of fixed size to the subscribers of the messaging service. So if a subscriber rapidly receives a large number of messages or does not regularly retrieve received messages, there is a good chance that the capacity of the subscriber's mailbox will be exceeded and the mailbox will overflow. This results in loss of messages or inability of message senders to leave further messages for the subscriber. Yet other subscribers may no longer be using their mailboxes, or use only a small portion of their mailboxes' capacities, resulting in a waste of storage space.
Many voice and/or multimedia messaging systems have warning announcements which are provided to subscribers to advise them of the fill level of their mailboxes. While this is a worthwhile feature, it does not specifically help with the problem of mailbox overflow conditions. It can be very frustrating to a caller to be informed that the party they are trying to reach has a full mailbox. The result can be loss of business, loss of necessary information, and/or loss of productivity. Two other related problems, from the system administrator's point of view, are the allocation of storage space to mailboxes which are seldom or never fully utilized, and the persistence of logins and their associated mailboxes that are still in place for subscribers who have changed messaging systems or ceased to be subscribers. This last problem is especially of concern in very large systems and/or those designed for public service-provider use.
Some systems provide audits that the system administrator may use manually to provide a means for sizing mailboxes and for expiring logins. But this does not provide the prompt response to changing conditions that is desirable.